Water reuse is essential for long duration space missions. However, water recycle systems also provide a habitat for microorganisms and allow accumulation of chemical compounds which may be acutely or chronically toxic to mission crew members. Contaminant fate and accumulation in closed-loop water recycle systems is being investigated at the University of Colorado and Martin Marietta as part of the activities of the Center for Space Environmental Health (CSEH), a NASA Specialized Center of Research and Training (NSCORT). The water contaminant distribution research uses a scaled-down physical model of a water (shower, laundry, urine and/or condensate) recycle system to analyze for and model four “indicator” contaminants: viruses and bacteria, nitrogen species, and selected organic and inorganic compounds. The water recycle test bed is comprised of five or more individual water treatment processes linked in a closed loop, and spiked with chemical and biological contaminants. A “systems” approach has been used to define experiments and data which can be used to characterize the long-term, overall performance of the test bed.The water contaminant distribution research at CSEH will augment the shorter-term investigations and individual process research being conducted by NASA at the Ames, Johnson, and Marshall Space Flight Centers.